Made loud pop an then grinding noise .. now just grinds an won't go.4x4 or 2hi

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Made loud pop an then grinding noise when started to pull in 4lo reverse.. now when start truck it makes grinding noise in P. R.N ... stoos n drive.. but wont go at all... sounded like popped out if gear when happened but now just grinds n 4hi.low an 2hi... had no trouble at all before